Dude. I can't give you any examples because I don't really watch porn, but SEIs are not at all rare in that kind of work. I also used to be semi-friends with an SEI stripper for what that's worth if it'll convince you that SEIs do sex work.
If you picture any kinda introverted slut (is that word offensive?), she's probably SEI.
Edit: there are different kinds of sluts of course so to clarify, IEIs are sluts to manipulate the men they sleep with, ESIs fall in lust with different men, one at a time, and SEIs are the school sluts who suck guys' dicks in the bathroom for the sheer pleasure and fun of it.